Fluid flow monitoring system of a geothermal reservoir by electrical prospecting

An advanced geophysical technique for reservoir monitoring by electrical prospecting has been developed by the joint research of Kyushu University and CRIEPI work in related to fracture evaluation at the Hot Dry Rock Geothermal Power Project in the Ogachi area. The Fluid Flow Tomography survey method utilizes a casing pipe itself as a charged current electrode similar to the mise-a-la-masse method. The method has been applied to monitor fluid-flow behaviors during massive hydraulic fracturing operations and fluid-circulation experiments from injection to production boreholes. In the automatic recording system controlled by a personal computer charged potentials (mV/A) and spontaneous potentials (mV) can be simultaneously measured as a function of time at multiple stations (120ch) surrounding an operating borehole. Fluid-flow behavior in the subsurface could be visualized as a function of time by using contour maps of residual potentials from SP data and relative changes of apparent resistivity due to dynamic reservoir stimulations.